Purifying bis(perfluoroalkyl) nitroxide

ABSTRACT

A method of purifying crude bis(perfluoroalkyl) nitroxide comprising contacting said crude nitroxide with mercury at a temperature between about -10 and 35*C. utilizing a reactant mole ratio of crude nitroxide of said mercury to said crude nitroxide of between about 1:10 and 100:1 to form a bis(perfluoroalkyl) nitroxide mercuride intermediate, separating said mercuride, and heating said separated mercuride at between about 50 and 100*C. to reform said mercury and bis(perfluoroalkyl) nitroxide and separating the reformed nitroxide from the reformed mercury.

tlnited States Patent [191 Reinhard et a1.

[ 51 Feb.27,19'73 [54] PURIFYING BIS(PERFLUOROALKYL) NITROXIDE [73]Assignee: Texaco Inc., New York, NY.

[22] Filed: Feb. 11, 1971 [21] Appl. No.: 114,713

Related 05. Application Data [62] Division of Ser. No. 811,119, March27, 1969, Pat.

[52] US. Cl ..260/583 D, 260/647, 260/701 [51] Int. Cl ..C07c 87/22 [58]Field of Search ..260/583 D, 647, 701

[56] References Cited UNITED STATES PATENTS 3,200,158 8/1965 Blackley..260/647 Crawford, Jr ..260/647 X Hoffmann ..260/583 D X PrimaryExaminer-Le1and A. Sebastian Att0rney-l(. E. Kavanagh et a1.

[57] ABSTRACT A method of purifying crude bis(perfluoroa1ky1) nitroxidecomprising contacting said crude nitroxide with mercury at a temperaturebetween about -10 and 35C. utilizing a reactant mole ratio of crudenitroxide of said mercury to said crude nitroxide of between about 1:10and 100:1 to form a bis(per- 2 Claims, N0 Drawings PURIFYINGBISWERFLUOROALKYL) NITROXmE This is a division of Ser. No. 81 1,1 19,filed Mar. 27, 1969, now US. Pat. No. 3,644,449.

BACKGROUND OF INVENTION Bis(perfluoroalkyl) nitroxides and their methodof manufacture are described in US. Pat. No. 3,200,158 and arecharacterized by the formula (R NO where R; is a perfluoro-saturatedaliphatic radical of from 1 to 12 carbons. They are further described inthe patent as paramagnetic (free radical) compounds which areparticularly useful as inhibitors in polymerization reaction, andtherefore, suitable as stabilizers in amounts of between 0.001 and 2 wt.in nylon and rubber compositions.

Although the bis(perfluoroalkyl) nitroxides are relatively stable, theydo tend to deteriorate after extended periods of storage at the warmeratmospheric temperatures. Further, the lower molecular weight nitroxidesare gases or liquids at room temperature which forms by their naturerequire more costly storage facilities than the solid form. It is,therefore, desirable to develop a means of storing the definedbis(perfluoroalkyl) nitroxides in solid form over lengthy periods suchas several months without any significant deterioration, that is, lessthan 1 wt. percent decomposition.

SUMMARY or INVENTION We have discovered, and this constitutes ourinvention, a novel product, namely, bis(perfluoroalkyl) nitroxidemercuride characterized by the formula [(R;) ],I-Igwhere x is l to 2prepared by contacting under conditions of agitation paramagneticbis(perfluoroalkyl) nitroxide of the formula (R,) NO' at a tem peraturebetween about-l and 35C.

The bis(perfluoroalkyl) nitroxide mercurides have the properties ofbeing a solid and of greater stability (up to 50C.) than theirbis(perfluoroalkyl) nitroxide precursors yet readily regenerable intothe corresponding precursor and mercury at temperatures of above 50 andup to 100C. and higher. Therefore, the formation of the mercury adductof bis(perfluoroalkyl) nitroxide is a convenient way of storingbis(perfluoroalkyl) nitroxide for long periods of time under extremelystable conditions. Further, as an ancillary benefit, the procedure ofconverting the bis(perfluoroalkyl) nitroxide to the mercury adduct andthen regenerating the adduct to its nitroxide precursor facilitatespurification of the nitroxide since gaseous, liquid and solid impuritiescanbe separated therefrom when it is in its solid mercuride form.

DETAILED DESCRIPTION OF THE INVENTION More specifically, we have found anovel compound of the formula: [(R,) NO],I-Ig where R, is aperfluorosaturated aliphatic radical (perfluoroalkyl) of from one to 12carbons and x is l to 2. The novel compounds are prepared by the newlydiscovered method of contacting bis(perfluoroalkyl) nitroxide of theformula (R,) NOwhere R; is as heretofore defined with the mercury metalat a temperature of between about l0 and 35C. under conditions ofagitation utilizing a mole ratio of bis(perfluoroalkyl) nitroxide tomercury of between about and 1:100. The presence of excess mercury inrespect to nitroxide reactant in the reaction system favors theproduction of a mercurous product, i.e., where Fl. In contrast, anexcess of nitroxide reactant in the system favors the production of amercuric product, i.e., where x==2. The reaction pressure may range fromsubatmospheric to superatmospheric, e.g., 1 mm. Hg. abs. to 10atmospheres. Normally when a mercuric product is desired and thenitroxide reactant is gaseous, said reactant is desirably maintainedunder superatmospheric pressure in said system. The reaction period isnormally between about 0.5 and 2.0 hours although a greater or lessertime may be employed depending upon the particular yield desired.

The products are silver grayish solids and are recovered from thereaction mixture by standard means such as filtration. Handling andstorage of the mercuride product should be carried out in the absence ofmoisture or protonic acids as these cause its ready conversion tobis(perfluoroalkyl) hydroxylamine.

The mercuride adducts are regenerated into their respective mercury andnitroxide components by heating the adducts at temperatures betweenabout 50 and 100C. and higher, preferably between 55 and 80C.

One of the important features in the method of the invention is themaintenance of the reaction ingredients under agitation conditions. Forexample, where the reaction is a liquid-gas or liquid-liquid contact,i.e., the mercury being in the liquid state and the bis(perfluoroalkyl)nitroxide in the gaseous or liquid state, sufficient agitation isnormally supplied by the stirring of the liquid reactant phase even whenblanketed by a gaseous reactant phase. If the reactants are notmaintained in an agitated contact then the yield of product issignificantly reduced. For example, when the nitroxide reactant phase isgaseous and the mercury component is not agitated, .a product film isformed on the surface of the mercury preventing extensive reaction.

Examples of the bis(perfluoroalkyl) nitroxide reactants contemplatedherein are bis(trifiuoromethyl) nitroxide, bis(perfluoroethyl)nitroxide, bis(perfluorot-butyl) nitroxide, bis(perfluoro-2-methylhexyl)nitroxide, bis(perfluoroheptyl) nitroxide, and bis(perfluorododecyl)nitroxide. Corresponding adduct products are [(Rfi NOl Hg where R, is

trifluoromethyl, perfluoroethyl, perfiuoro-t-butyl,perfluoro-2-methylhexyl, perfluoroheptyl, perfluorododecyl and where xis l and where x is 2. When 1: is not a whole number this denotes amixture of x=l and x=2 product. For example, x=1.5 value denotes a 1:1mole mixture of x=l and x=2 product.

As heretofore stated, one of the ancillary benefits of the invention isthe purification of bis(perfluoroalkyl) nitroxide as well as its verystable storage. This purification is accomplished by sequentiallyconverting the bis(perfluoroalkyl) nitroxide to the mercuride isolatingthe mercuride, e.g., evacuating the atmosphere over i The followingexamples further illustrate the products, method of preparation,regeneration and purification embodiments of the invention but are notto be construed as limitations thereof.

EXAMPLE I (CF NOB.. In a total system volume of 140 ccs. the

pressure decreased from an original 12 mm. to 11.5 mm. Hg. abs. after 8minutes without stirring of the mercury. Subsequent stirring of themercury by the magnetic bar is accompanied by a decrease in the systempressure from 11.5 mm. to 2 mm. Hg. abs. and the formation of silvergray solid suspended in the excess mercury. The silver gray solid isanalyzed and found to be bis(trifluoromethyl) nitroxide mercuride of theformula [(CF NO] .,Hg. where x is 1.

EXAMPLE II This example illustrates the reversible nature of thenitroxide-mercury reaction.

A 50 ccs. round-bottomed Pyrex flask is charged with 3 ccs. of purifiedmercury and a Teflon coated stirring bar. After degassing the mercury,it is contacted with gaseous (CF NO- (67.2 ccs. at 100 mm. Hg. abs.) at25C. for 100 minutes with stirring. The unreacted gases (44 mm. Hg. abs.in 140 ccs.) are evacuated from the resulting silver gray solidsuspended in excess mercury. The solid product is identified as [(CF),NO],Hg. where x is 1 having a heat of dissociation of 17.6 kcal./mole.The product is heated to l23C. and the products resulting from theheating are analyzed and determined to include mercury andbis(trifluoromethyl) nitroxide.

EXAMPLE m This example illustrates the preparation and use of themercuride product [(R,),NO],Hg. as a convenient source of its nitroxideprecursor (R,) NO' in purified form.

A 50 ccs. round-bottomed Pyrex flask is charged with 5 ccs. of purifiedmercury and the whole is carefully degassed and dried under high vacuum.Crude bis(trifluoromethyl) nitroxide (109 mm. Hg. abs. in 67.2 ccs.) isintroduced into the flask while stirring the mercury at 25C. After onehour, essentially all of the nitroxide is reacted and the CO N 0, CF,,CF NO CF N%F,, and (CF NOH impurities associated with the crudenitroxide reactant are removed by the application of high vacuum to thereactor flask leaving a silver gray solid residue which is determined tobe [(CF NO],Hg. where x is 1. Heating the flask at 65 to C. for 30minutes while stirring the contents and evacuating through a liquidnitrogen cooled cold trap decomposes the silver gray product in theflask and yields a yellow solid in the cold trap which on warming toroom tem erature amounts to 67.2 ccs. (98 mm. Hg. abs.) of (C NO- whichshows no impurities by 1nfrared or gas chromotographic analysis.

The above procedure is repeated with the exception the nitroxide isintroduced under l0 atmospheres into a pressure flask in mole excess ofthe mercury present. The results are the same except the solid residueis determined to be [(CF NO],Hg. where x is 2.

EXAMPLE IV This example illustrates the preparation of the mercurideproduct from impure nitroxide and the regeneration of purified nitroxidefrom the solid mercuride product.

A 50 ccs. round-bottomed Pyrex flask is charged with 5 ccs. of purifiedmercury and a magnetic stirring bar. After degassing under high vacuum,the mercury is contacted while stirring with impure (CF NO- (109 mm. Hg.bas.). After stirring 19 minutes at room temperature, the residual gasis condensed in the flask at -l96C. On warming and after stirring foranother 5 minutes, only 1 mm. Hg. abs. of residual gas remained in thesystem (140 ccs.). The flask is evacuated and is then heated at 65 to70C. while pumping the evolved gases through a liquid nitrogen cooledtrap. After all the gray solid in the flask is decomposed and only athin dark film remains on the mercury pool, the liquid nitrogen cooledcold trap is isolated and is warmed to yield a purple gas (98 mm. Hg.abs.) which is shown to be pure (CF ),NO- by infrared analysis.

We claim:

1. A method of purifying crude bis(perfluoroalkyl) nitroxide of theformula (R,) NO- where R, is perfluoroalkyl of from one to 12 carbonscomprising contacting said crude bis(perfluoroalkyl) nitroxide withmercury under conditions of agitation at a temperature between about 10and 35C. utilizing a reactant mole ratio of said mercury to said crudebis(perfluoroalkyl) nitroxide of between about l:l0 and 100:1 to formbis(perfluoroalkyl) nitroxide mercuride of the formula [(R,) ,Hg wheresaid R, is as heretofore defined and x is an integer from 1 to 2inclusively, separating said mercuride from the reaction mixture,heating said separated mercuride at a temperature of between about 50and 100C. to reform said mercury and said bis(perfluoroalkyl) nitroxideof the formula (R,),NO- and separating said reformed nitroxide in apurified state from said reformed mercury.

2. A method in accordance with claim 1 wherein said R,is perfluoromethyland said x is l.

2. A method in accordance with claim 1 wherein said Rf isperfluoromethyl and said x is 1.